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Merge

Merging sequences is the operation consisting of listening for values from several
Publishers and emitting them in a single Flux.

On this first exercise we will begin by merging elements of two Flux as soon as they arrive.
The caveat here is that values from flux1 arrive with a delay, so in the resulting Flux
we start seeing values from flux2 first.

Simple Merge

But if we want to keep the order of sources, we can use the concat operator. Concat will
wait for flux1 to complete before it can subscribe to flux2, ensuring that all the values
from flux1 have been emitted, thus preserving an order corresponding to the source.

Keep the order

You can use concat with several Publisher. For example, you can get two Mono and turn
them into a same-order Flux: